Methods of manufacturing fibrous granulates

ABSTRACT

This invention relates to methods of manufacturing fibrous granulates. Various fibers of animal, vegetable, mineral or synthetic origin can be granulated by a method in accordance with the invention in which the fibers are first intertangled or felted in a dry state and then tightened relative to each other by treatment with a liquid followed by drying. The liquid is used in an amount which is sufficient to form menisci between the fibres. Additional bonding between the fibers can also be effected using bonding agents etc. The present invention enables fibrous granulates to be produced which are coherent, substantially spherical, light, flexible and resilient.

Jacquelin et a1.

Assignee:

METHODS OF MANUFACTURING FIBROUS GRANULATES Inventors: Guy Jacquelin,Grenoble; Jean Fournet, Saint-Romain-en-Gal, both of France Societed'Exploitation des Brevets Granofibre Sebreg, Ampuis, France Filed: July13 1973 App]. No.: 378,899

Foreign Application Priority Data July 21, 1972 France 72.26426References Cited UNITED STATES PATENTS 10/1949 Francis, Jr. 264/1221/1966 Harrington, Jr. ct al. 264/122 [451 Sept. 9, 1975 3,564,0832/1971 Foumet ct a1. 264/37;1I7 X 3,589,977 6/1971 Foumet et al. 162/9Primary IirarriinerMelvin Goldstein Assistant Examiner-Thomas DeBenedictis Attorney, Agent. or Firm-Lewis H. Eslinger; Alvin Sinderbrand57 1 ABSTRACT This invention relates to methods of manufacturing fibrousgranulates. Various fibers of animal, vegetable, mineral or syntheticorigin can be granulated by a method in accordance with the invention inwhich the fibers are first intertanglcd or felted in a dry state andthen tightened relative to each other by treatment with a liquidfollowed by drying. The liquid is used in an amount which is sufficientto form menisci between the fibres. Additional bonding between thefibers can also be effected using bonding agents etc. The presentinvention enables fibrous granulates to be produced which are coherent.substantially spherical. light, flexible and resilient.

1! :Claims, No Drawings METHODS OF MANUFACTURING FIBROUS GRANULATES Thisinvention relates to methods of manufacturing fibrous granulates.

It has hitherto been proposed to manufacture fibrous granulates in twostages, firstly by subjecting the fibres to a dry treatment in whichindividual fibers assembled loosely in a tunnel having a horizontal axisare stirred by rotation of the tunnel so as to startimbrication of thefibers into groups and to form fibrous aggregates having littlecohesion, and then to treat the aggregates with a liquid carrier duringwhichthe aggregates are suspended in a liquid and agitated with thisliquid either by simple rotation or rotation combined with pulsation toconsolidate the fibrous aggregates and transform them into granulateshaving desired properties.

The products of such a method are desirably coherent, substantiallyspherical, light, flexible and resilient fibrous granulates which aresufficiently solid not to come apart easily, and are relativelyinexpensive to produce from the base fibers.

According to the prescntiinvention there is provided a method ofmanufacturing a fibrous granulate which method comprises agitatingnatural or synthetic fibers which are dry on their surface and have amoisture content of not more than 55% of the total weight of the fibersunder dry conditions in order to initiate their imbrication in groupsand form fibrous aggregates having little cohesion; depositing a liquidon the surface of the aggregates so as to form liquid menisci betweenthe surfaces of the fibers of each aggregate and cause tighten ing ofthe fibers; and evaporating the liquid to intensify the tightening.

The fibers may be of natural origin, for example vegetable fibers suchas wood fibers, annual plant fibers e.g. straw, cotton linters or thelike; animal fibers such as wool or various hairs; or mineral fiberssuch as asbestos or various fibrous crystals. The fibers may also be ofartificial origin, for example organic fibers such as viscoses orrayons; or mineral fibers such as spun glass or stone or the like. Thefibers in addition may be of synthetic origin such as polyvinylchloride, a polyolefin, a polycarbonate, or one of various copolymers.

As used herein, the word aggregate refers to organised groups of fibersobtained by dry treatment and the word granulate refers to spherulesobtained by consolidation of such aggregates.

Using a method in accordance with the present invention it is possibleto reduce the duration of the wet treatment of the aggregates comparedwith hitherto, the energy consumed in effecting this treatment and theenergy in extracting water from the granulates. The cost of theresulting granulates can thereby be reduced considerably;

Apparatus for effecting a method in accordance with the invention can besimpler than that used for hitherto proposed methods and this makes itpossible to reduce the amount of capital investment in the apparatus andthis influences the cost of the granulates. Furthermore, it is possibleto establish profitable small capacity installations near to placeswhere the fibrous granulates are produced.

Where the product is to consist only of fibrous granulates, the fibrousmass resulting from the dry treatment will generally be graded in orderto separate the fibrous aggregates of desired size from othercomponents.

These other components can be pulverulent products, fibers that haveremained free, and fibrous groups that are loose or are of unsuitablesize. The fibrous groups tend to disintegrate and completely free thefibers that consitute them. The free fibers removed during separa' tionand the free fibers produced by disintegration, can be mixed with freshfibers and subjected to a dry treat ment. The liquid is then onlydeposited on fibrous aggregates which have been graded.

Fibrous aggregates extracted from the fibrous mass resulting from thedry treatment are preferably spread in a layer of substantially uniformthickness and the liquid atomized on to this layer while the aggregateis being vibrated. I

The liquid may be water which may, if desired, contain a surfactantand/or a binder.

The fibrous granulates are advantageously dried after moistening.

In a practical embodiment of the present invention, the fibers used weredistinct from one another, al though in the case of vegetable fibers,the mass of fibers treated contained afew slivers, that is to thickbundles of fibers in which numerous parallel fibers are connected to oneanother and constitute a group that does not have the form of a fiber.

Irrespective of the origin of the fibers, which maybe animal, vegetable,mineral or synthetic, the fibers were dry. The fibers were not moist ontheir surfaces at this stage but they could have internal moisture.Thus, in the case of wood fibers, the moisture contentcould be from 3 to55% of the total weight of the fibers but it should not make them appeardamp to the touch.

For the dry treatment, the individual dry fibers were assembled in atunnel in the form of a body with a horizontal axis of revolution. Thetunnel may have partitions. The tunnel was arranged to be driven inrotation about its horizontal axis. The tunnel was filled to more thanhalf its internal volume. Moreover, no liquid was distributed in thistunnel, so that the treatment of the fibers was carried out under reallydry conditions.

The fibers were subjected to mechanicalfelting interactions duringrotation of the tunnel. The fibers were slightly deformed resilientlyand their interlacing was consolidated by the stresses developed bythese resilient forces. Fibrous aggregates were thus formed in themoving mass of fibers undergoing treatment.

Most of the resulting cohesive aggregates, which were in the form ofspherules, had dimensions which corresponded substantially to the meanlength of the fibers and these dimensions varied little even when thetreatment was prolonged. Moreover, the fibrous structures that wereformed were cohesive only in so far as their dimensions did not greatlyexceed the mean length of the fibers. Larger structures had a tendency.to break during sliding of the layers of fibers relative to one another,and when'falling.

The effectiveness of the dry treatment generally depends on the extentto which the tunnelis filled, since the active driving surface must besmall with respect to the volume'treated, and on the speed of rotationofthe tunnel.

Particularly good results were obtained whenthe. extent of filling ofthetunnel was between two thirds and four fifths of the volume of thetunnel.

For example, when 85.0kg. of weed fibers are subjected to the drytreatment in a tunnel 2.5m in diameter and 8m long, the extent offilling is 65%. After 2 hours rotation at a peripheral speed of about8(lm/min. 80% of the fibrous mass had been transformed into aggregates.

When the grain size of the aggregates had been stabilized, the drytreatment was complete and the wet treatment could begin.

Although not always necessary. it may be found desirable to grade thetreated fibrous mass before it is subjected to the wet treatment inorder to separate fibrous aggregates of appropriate sizes. fibers thathave remained free. fibrous groups that are loose or are of unsuitablesize, and pulverulent products and the like.

This grading may be effected by screening. which also makes it possibleto eliminate fibrous aggregates of appropriate size which haveinsufficient cohesion. These latter aggregates tend to fail to withstandthe various stresses imposed by the screens, and they break The groupsthat are loose, or are of unsuitable size. and the remains of aggregatesdestroyed during screening. are disintegrated. for instance by carding.so that the fibers of which they are made are freed from one another.These fibers. and those that remained free. can be mixed with fibersbeing used for the first time and subjected to a fresh dry treatment sothat fibers that are not aggregated or are badly aggregated arerecycled.

The graded fibrous aggregates cannot be used in such a state becausetheir internal cohesion is insufficient.

It is therefore essential to consolidate the aggregates and the wettreatment hereinafter described enables this to be effected.

The wet treatment is preferably applied to fibrous aggregates which havebeen separated from the rest of the mass that has been subjected to thedry treatment. However. the wet treatment can be applied to the whole ofthe mass. provided that the product containing the granulate can containfree fibers or loose groups of fibers. and also provided that theproportion of fi brous aggregates in the mass is sufficiently high.

The wet treatment consists of depositing a quantity of a liquid on thesurface of the fibrous aggregates which is just sufficient to formliquid menisci between the surfaces of the fibers. These menisci causetightening of the fibers and this tightening is intensified byevaporation of the liquid.

Advantageously the fibrous aggregates are spread in a layer ofsubstantially uniform thickness on a moving surface and the liquiddistributed by atomization. In order to provide uniform moistening, themoving surface is preferably vibrated. The moving surface, which may behorizontal. rising or falling, and may be flat. cylindrical, helical orof some other shape, guides the suitably moistened fibrous aggregatestowards a dryer so that the liquid forming the menisci is completely andrapidly removed.

In most cases, and more particularly when the base fibers are of naturalorigin, the liquid can be water. The mean moisture content of the wholemass is then preferably between 50 and 85% based on the total weight ofthe moist aggregates.

in certain cases, however, other liquids can be sprayed on. For example,if the base fibers are polyethylene the liquid may be a hydrocarbonor asolvent which moistens the fibers.

To show clearly the transformation which results from the wet treatment.and by which the fibrous ag- 4 gregates having little cohesion becomefibrous granulates having better cohesion, two types of tests have beeneffected.

A first series of tests was designed to measure the diametricalcontraction of the fibrous aggregates subjected to wet treatment.Aggregates based on wood fibers were disposed on a motionless plate, andthe variation in the diameter of a large number of aggregates wasmeasured by means of a cathctorneter.

Atomization of water was found to be accompanied by a contractionvarying from 5 to lO /z. according to the aggregates. and drying wasaccompanied by a further contraction of about 1%.

A second series of tests was designed to measure the cohesion of thefibrous granulates. Two needles were inserted diametrally into eachgranulate. Then, by means of a dynamometer, a force tending tomove theneedles apart was exerted until the granulate subjected to the testdisintegrated. The value of the breaking force. arbitrarily called thecohesion. is significant and was given as a criterion of estimation. Theexample described hereinafter refers to the results of several tests.

Fibers of conifers such as those which make up wood pulp" paste weresubjected to a dry treatment in accordance with the invention. Thefibrous aggregates obtained had weak cohesion because the cohesion wasbetween and 12g for a diameter of 8mm.

The aggregates were moistened to 80% with water. and then dried. Thecohesion of the fibrous granulates obtained was then between and g.

It may be advantageous to reinforce the effect of moistening, whichresults in producing a physical and mechanical effect in which thefibers of the aggregates are tightened. by combining the effect ofmoistening with that of another kind of connection between the fibcrs.

Reinforcing connections can be produced by moistening with the liquid.In this case the liquid serves to swell the surface fibers, and if thesefibers have been brought sufficiently close together under the action ofthe surface tensional forces. connections between fibers appear andthese further consolidate the granulates.

For example, if polymer fibers are to be treated, a swelling agent whichpermits bonding by evaporation may be used in the moistening liquid.

With certain thermoplastic fibers, the granulates can be subjected to athermal treatment which makes it possible to accelerate evaporation ofthe moistening liquid and the drying of the granulates. Furthermore, itisthereby possible to soften the surface of the fibers and produce ontheir surfaces a pasty state similar to that obtained using a swellingagent. The interfacial tension forces than produce local welding bybringing the fibers close together.

For example. 5 to 8mm diameter polyvinyl chloride granulates having acohesion of a few grammes between needles may attain a cohesion of morethan 800g when subjected to thermal treatment for a few minutes at to C.

Fibers which are thermocontractile, and react to an increase intemperature by changing their dimensions can be subjected to a-thermaltreatment in the form of a granulate which also makes it possible toaccelerate evaporation of the moistening liquid and the drying of thegranulate. to produce intensified imbrication and tightening of thefibers.

5 In general. the moistening liquid used with any type of fiber caninclude a substance capable of consolidating the approach of the fiberstowards one another by glued connections. It is possible for thispurpose to use various amylaceous materials. various polymers and moregenerally any product capable of producing a glued connection betweenthe fibers by drying and/or thermal treatment. For example. fibrousaggregates obtained by dry treatment of conifer fibers can be moistenedwith a 2()g/l suspension of pro-gelled starch in water so that theirweight is doubled.

After drying. the cohesion of the fibrous granulates thus obtained canreach a value between 80 and l()()g.

A method in accordance with the invention may be used in most cases inwhich the fibrous granulates are required to be economical and are notsubjected to tensile stresses or are only subjected to weak tensilestresses.

Particularly important applications are the manufacture of light. porousinsulating fillers and the manufacture of base products for theproduction of moulded or extruded parts forming sub-layers of variouscoatings.

We claim:

1. A method of manufacturing a fibrous granulate. which method comprisesthe steps of agitating resilient fibers which are dry on their surfacesand which have a moisture content of not mre than 55% of the totalweight of the fibers under dry conditions, to initiate imbrication ofthe fibers in groups and form fibrous aggregates'having relatively lowcohesion; thereafter depositing on the surface of the fibrous aggregatesa suitable liquid selected. in accordance with the fibers being treated.to form liquid menisci on the fibers; said depositing step comprisingthe step of spraying only a limited amount of liquid onto the fibrousaggregates which limited amount of liquid is just sufficient to formliquid menisci between the surfaces of the fibers of each aggregate atthe crossing points of the fibers, thereby to deform the fibers andcause mechanical tightening and increased mechanical interengagemcnt andcohesion of the fibers; and thence evaporating the liquid to intensifythe tightening and increase the mechanical interengagement and cohesionof the fibers.

2. A method according to claim 1, wherein said agitating step comprisesagitating the fibers in a rotary tunnel having a substantiallyhorizontal axis, the tunnel being filled with fibers to between twothirds and four fifths of its volume.

3. A method according to claim 1, including the steps of grading thefibrous mass resulting from the dry agi tating step before saiddepositing step to separate fibrous aggregates of a predetermined sizefrom pulverulent products. fibers that have remained free. loose fibergroups and fiber groups of less than a predetermined size. thereafterdisintegrating the fiber groups to free the fibers that constitute them.collecting the free fibers removed during the grading step and the freefibers obtained by said disintegrating step and mixing the collectedfree" fibers with fresh fibers and subjecting them to the dry agitatingstep. and depositing said liquid solely on the fibrous aggregates ofpredetermined size separated during the grading step.

4. A method according to claim 1. wherein said dcpositing step comprisesatomizing the liquid on the fibrous aggregates.

5. A method according to claim 3 including the steps of spreading theseparated fibrous aggregates in a layer of substantially uniformthickness and vibrating the ag gregates during distribution of theliquid.

*6. A method according to claim 1. including the step ofdrying thefibrous aggregates after distribution of the liquid.

7. A method according to claim 1. wherein the liquid deposited on thefibrous aggregates is water and the mean moisture content thereof afterdeposition is from 50 to 8571 based on the total weight of the moistaggregates.

8. a mcthodaccording to claim 1. including the step of formingadditional connections between the fibers to reinforce the physical andmechanical action of tightening of the fibcrs'due to dampening with theliquid.

9. A method according to claim 8. wherein the fibers are thermoplasticand additional connections are ob tained by subjecting fibers tightenedby the liquid to a thermal treatment which produces local weldingbetween the fibers.

10. A method according to claim 8. wherein the fibers arethcrmocontractile and the additional connections are obtained bysubjecting the granulates tightened by the liquid to a thermal treatmentwhich intensifies this tightening.

1 1. A method according to claim 8, wherein the damping liquid containsa binding agent which causes localised gluing between the fibers whenthe granulates tightened by this liquid are dried and additionalconnections are thereby produced.

1. A METHOD OF MANUFACTURING A FIBROUS GRANULATE, WHICH METHOD COMPRISESTHE STEPS OF AGITATING RESILIENT FIBERS WHICH ARE DRY ON THEIR SURFACESAND WHICH HAVE A MOISTURE CONTENT OF NOT MORE THAN 55% OF THE TOTALWEIGHT OF THE FIBERS UNDER DRY CONDITIONS. TO INITIATE IMBRICATION OFTHE FIBERS IN GROUPS AND FROM FIBROUS AGGREGATES HAVING RELATIVELY LOWCOHESION, THEREAFTER DEPOSITING ON THE SURFACE OF THE FIBROUS AGGREGATESA SUITABLE LIQUID SELECTED, IN ACCORDANCE WITH THE FIBERS BEING TREATED,TO FORM LIQUID MENISCI ON THE FIBERS, SAID DEPOSITING STEP COMPRISINGTHE STEP OF SPRAYING ONLY A LIMITED AMOUNT OF LIQUID ONTO THE FIBROUSAGGREGATES WHICH LIMITED AMOUNT OF LIQUID IS JUST SUFFICIENT TO FORMLIQUID MENISCI BETWEEN THE SURFACES OF THE FIBERS OF EACH AGGREGATE ATTHE CROSSING POINT OF THE FIBERS, THEREBY TO DEFORM THE FIBERS AND CAUSEMECHANICAL TIGHTENING AND INCREASED MECHANICAL INTERENGAGEMENT ANDCOHESION OF THE FIBERS, AND THENCE EVAPORATING THE LIQUID TO INTENSIFYTHE TEGHTENING AND INCREAASE THE MECHANICAL INTERENGAGEMENT AND COHESIONOF THE FIBERS.
 2. A method according to claim 1, wherein said agitatingstep comprises agitating the fibers in a rotary tunnel having asubstantially horizontal axis, the tunnel being filled with fibers tobetween two thirds and four fifths of its volume.
 3. A method accordingto claim 1, including the steps of grading the fibrous mass resultingfrom the dry agitating step before said depositing step to separatefibrous aggregates of a predetermined size from pulverulent products,fibers that have remained free, loose fiber groups and fiber groups ofless than a predetermined size, thereafter disintegrating the fibergroups to free the fibers that constitute them, collecting the freefibers removed during the grading step and the free fibers obtained bysaid disintegrating step and mixing the collected free fibers with freshfibers and subjecting them to the dry agitating step, and depositingsaid liquid solely on the fibrous aggregates of predetermined sizeseparated during the grading step.
 4. A method according to claim 1,wherein said depositing step comprises atomizing the liquid on thefibrous aggregates.
 5. A method according to claim 3 including the stepsof spreading the separated fibrous aggregates in a layer ofsubstantially uniform thickness and vibrating the aggregates duringdistribution of the liquid.
 6. A method according to claim 1, includingthe step of drying the fibrous aggregates after distribution of theliquid.
 7. A method according to claim 1, wherein the liquid depositedon the fibrous aggregates is water and the mean moisture content thereofafter deposition is from 50 to 85%, based on the total weight of themoist aggregates.
 8. a method according to claim 1, including the stepof forming additional connections between the fibers to reinforce thephysical and mechanical action of tightening of the fibers due todampening with the liquid.
 9. A method according to claim 8, wherein thefibers are thermoplastic and additional connections are obtained bysubjecting fibers tightened by the liquid to a thermal treatment whichproduces local welding between the fibers.
 10. A method according toclaim 8, wherein the fibers are thermocontractile and the additionalconnections are obtained by subjecting the granulates tightened by theliquid to a thermal treatment which intensifies this tightening.
 11. Amethod according to claim 8, wherein the damping liquid contains abinding agent which causes localised gluing between the fibers when thegranulates tightened by this liquid are dried and additional connectionsare thereby produced.